Figure 4. The packing density/affinity relationship for barbiturates is offset from that of the propofol-like compounds, interpreted here as the addition of an entropic penalty offset by new enthalpic gains.

Shown is the relationship between packing volume (fraction of cavity volume occupied by ligand) and affinity (dissociation constant, K _d) for apoferritin. The filled triangles represent a series of propofol analogs, for which a linear dependence of affinity upon packing density has been documented [21]. The open circles represent the barbiturates (P, pentobarbital; T, thiopental).